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Date: Tue, 1 Feb 2011 10:08:33 -0800
From: Jesse Barnes <jbarnes@virtuousgeek.org>
Cc: Hugh Dickins <hughd@google.com>, Chris Wilson <chris@chris-wilson.co.uk>,
        Mario Kleiner <mario.kleiner@tuebingen.mpg.de>,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] drm/i915: Suppress spurious vblank interrupts
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On Tue, 1 Feb 2011 09:46:43 -0800
Jesse Barnes <jbarnes@virtuousgeek.org> wrote:

> On Tue, 1 Feb 2011 09:34:12 -0800 (PST)
> Hugh Dickins <hughd@google.com> wrote:
> > As you know (I went off-list to send more info at the weekend), this
> > behaviour is very elusive, probably depends on more than one issue,
> > comes and goes with irrelevant patches and config changes and reboots.
> 
> Are you still seeing underruns during normal activity?  I wonder if the
> ones you were seeing before were only reported at 60Hz due to vblank
> interrupt processing.  If we failed to clear the underrun status, we'd
> report one every time we got a vblank interrupt (since the underruns
> don't report interrupts by themselves).
> 
> If so, that may just be a red herring in this case.

More random questions arise from the info provided:
 - why are we ending up in the flip code at all?  fvwm shouldn't
   trigger that path...
 - what's with all the underruns?  it looks like we *do* ack those
   flags as needed, so apparently they're valid, but they indicate a
   serious problem with the display pipeline; maybe self-refresh
   shouldn't be enabled on your system (that would increase memory
   latency and potentially cause underruns), running with
   i915.powersave=0 would disable that feature

The lack of text really does sound like a render cache flushing
problem, but the other issues are worrying as well, and could be
compounding things.  And the last time I saw the issue, it was related
to compositing and required an X server fix.  But supposedly you're not
using compositing, so...

-- 
Jesse Barnes, Intel Open Source Technology Center
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